The present invention relates to a novel liquid-crystalline compound which is a naphthalene derivative useful as an electro-optical liquid crystal display material, a liquid crystal composition containing such naphthalene derivatives and a liquid crystal display device comprising the same.
A liquid crystal display device has been used more and more in watch and electronic calculator as well as various measuring instrument, panel for automobile, word processor, electronic note, printer, computer, television, etc. Representative examples of liquid crystal display system include TN (twisted nematic) system, STN (super-twisted nematic) system, DS (dynamic scattering) system, GH (guest-host) system, and FLC (ferroelectric liquid crystal) system, which allows high speed response. Referring to driving system, multiplex driving has been more common than the conventional static driving. Further, simple matrix system has been recently put into practical use. Moreover, active matrix system has been put into practical use.
As the liquid crystal materials to be incorporated in these liquid crystal display devices there have been synthesized a very large number of kinds of liquid-crystalline compounds to date. These liquid-crystalline compounds are used depending on their display systems, driving systems or purposes. However, the requirement for improvement of the properties of liquid crystal display device (enhancement of display quality or increase of the size of display) has been growing more and more. In order to satisfy these requirements, the development of new liquid crystal compounds are under way.
A liquid crystal compound is composed of a central skeleton moiety generally called care and a terminal moiety at both ends thereof. In general, the majority of the ring structure constituting the core moiety of a liquid crystal compound is occupied by 1,4-phenylene group (which may be substituted by one or two halogen atoms, cyano groups, methyl groups, etc.) and trans-1,4-cyclohexylene group. However, a liquid-crystalline compound merely made of 1,4-phenylene group and trans-1,4-cyclohexylene group is limited in its kind or properties. As a matter of fact, these components cannot sufficiently meet the foregoing demands.
Besides the ring structures such as 1,4-phenylene group and trans-1,4-cyclohexylene group, heterocyclic groups such as pyridine-2,5-diyl group, pyrimidine-2,5-diyl group and 1,3-dioxane-trans-2,5-diyl group, condensed rings such as trans-decahydronaphthalene-2,6-diyl group, naphthalene-2,6-diyl group, tetrahydronaphthalene-2,6-diyl group, bicyclo[2,2,2]octane-1,4-diyl group and spiro[3,3]heptane-2,6-diyl group, etc. have been under study. However, few of these compounds have been put into practical use due to problems in production (technique, cost, etc.) and stability.
Though being a ring structure which has long been reported, naphthalene-2,6-diyl group among these condensed rings is little known for properties other than liquid crystallinity (phase transition temperature), particularly nematic liquid crystallinity. (For smectic liquid crystal, it has recently been reported that an optically active alcohol ester of naphthalenecarboxylic acid exhibits interesting properties an a ferroelectric liquid crystal.)
An ordinary liquid crystal compound in terminated by a chain (side chain) group at one end thereof at least. A so-called p-type liquid crystal the dielectric anisotropy of which is positive is mostly terminated by a polar group at the other end thereof.
In order to lower the driving voltage in TN or STN display system, a so-called strong P-type compound (the dielectric anisotropy of which is positive and great) is required. For this purpose, a compound terminated by cyano group at the molecular end thereof and having one or more fluorine atoms in the same direction per molecule is normally used. An a naphthalene derivative there has been reported only a compound having phenylnaphthalene skeleton (GB2271771A: Citation (a)). There is no reference to physical properties and application.
As the foregoing P-type compound to be used in active matrix driving there is used a compound containing as a polar group fluorine atom, fluoroalkoxyl group or fluoroalkyl group alone. As a naphthalene derivative there is described only a compound having phenylnaphthalene skeleton in GB2227019B (Citation (b)) and the above Citation (a). However, there in little reference to specific physical properties. Further, there is no reference to application to active matrix system.
In general, a liquid-crystalline compound which is a naphthalene derivative mostly exhibits a poor miscibility with other liquid crystal compounds. It is thought effective to introduce side substituents (preferably fluorine atom in particular) into the naphthalene skeleton for the purpose of improving the miscibility of the naphthalene derivative. The substitution by fluorine atom is thought effective also if an end polar group is directly introduced into the naphthalene ring in the application to the foregoing active matrix system. Some examples of such a fluoronaphthalene derivative are shown in the foregoing Citation (a). However, there is little reference to production process, not to mention physical properties. Thus, it is by no means thought that these exemplified compounds are actually produced compounds. Further, it cannot be presumed what properties these compounds have. No compounds having a structure having a fluoroalkoxyl group or fluoroalkyl group directly connected to naphthalene ring as a polar group have been known,
It has been known that a liquid crystal compound having an alkenyl group instead of an alkyl group, which is normally used as a side chain moiety, exhibits excellent improvements such as improved liquid crystallinity, reduced viscosity and improved sharpness in display. However, these alkenyl groups are mostly introduced directly connected to cyclohexane ring. Thus, no compounds having alkenyl groups introduced in naphthalene ring have been reported.
Similarly, no naphthalene derivatives having as side chain alkoxylalkyl group, fluoroalkyl group, fluoroalkenyl group, fluoroalkenyloxy group, etc. have been reported.
As groups connecting the ring structures in the core moiety of a liquid crystal compound, there have been known many divalent organic groups besides single bond and 1,2-ethylene group (xe2x80x94CH2CH2xe2x80x94).
Liquid crystal compounds having 1,4-butylene group or 1,2-propylene group are known to have a low melting point and an excellent miscibility with other liquid crystal compounds as compared with the corresponding liquid crystal compounds having single bond or ethylene group. However, no liquid-crystalline compounds having 1,4-butylene group or 1,2-propylene group have been known among naphthalene derivatives.
It has been reported that a liquid crystal compound having difluoroxymethylene group (xe2x80x94CF2Oxe2x80x94, xe2x80x94OCF2xe2x80x94) or difluoroethenyl group (xe2x80x94CFxe2x95x90CFxe2x80x94) exhibits a low viscosity and thus is effective for the enhancement of response. However, no such naphthalene derivatives have been known.
An object of the present invention is to provide a novel liquid-crystalline compound having a naphthalene ring and a practical liquid crystal composition comprising the same.
The present invention has the following constitutions to accomplish the foregoing object:
1. A naphthalene derivative represented by the following general formula (I): 
wherein Ra represents a C1-20 alkyl, alkoxy, alkoxyalkyl, alkenyl or alkenyloxy group which maybe substituted by a C1-7 alkoxyl group or from 1 to 7 fluorine atoms; a and b each represent an integer of 0 or 1 and satisfy the relationship axe2x89xa6b; rings A and B each independently represent a trans-1,4-cyclohexylene group, 1,4-phenylene group which may be substituted by one or more fluorine atoms, pyridine-2,5-diyl group, pyrimidine-2,5-diyl group, pyrazine-2,5-diyl group, pyridazine-3,6-diyl group, trans-1,3-dioxane-2,5-diyl group, trans-decahydronaphthalene-2,6-diyl group or tetrahydronaphthalane-2,6-diyl group; La and Lb each independently represent xe2x80x94CH2C2xe2x80x94, xe2x80x94CH2CH2CH2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90CHCH2CH2xe2x80x94, xe2x80x94CH2CH2CHxe2x95x90CHxe2x80x94, xe2x80x94CH(CH3)CH2xe2x80x94, xe2x80x94CH2CH (CH3 )xe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94, xe2x80x94CF2Oxe2x80x94, xe2x80x94OCF2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94 or single bond; X1 to X6 each independently represent a hydrogen atom or fluorine atom; and Za represents a fluorine atom, chlorine atom, trifluoromethoxy group, C1-7 alkoxyl group, C1-20 alkyl, alkoxyl, alkenyl or alkenyloxy group which may be substituted by from 1 to 7 fluorine atoms or group represented by the following general formula (IIa) or (IIb): 
wherein Lc and Ld each independently represent xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2CH2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90CHCH2CH2xe2x80x94, xe2x80x94CH2CH2CHxe2x95x90CHxe2x80x94, xe2x80x94CH(CH3)CH2xe2x80x94, xe2x80x94CH2CH(CH3)xe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94, xe2x80x94CF2Oxe2x80x94, xe2x80x94OCF2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94 or single bond; rings C and D each independently represent a trans-1,4-cyclohexylone group, 1,4-phenylene group which may be substituted by one or more fluorine atoms, pyridine-2,5-diyl group, pyrimidine-2,5-diyl group, pyrazine-2,5-diyl group, pyridazine-3,6-diyl group, trans-1,3-dioxane-2,5-diyl group, trans-decahydronaphthalene-2,6-diyl group or tetrahydronaphthalene-2,6-diyl group; Zb and Zc each independently represent a fluorine atom, chlorine atom, bromine atom, iodine atom, hydrogen atom; cyano group, xe2x80x94SCN, xe2x80x94OCN, xe2x80x94Rxe2x80x2, xe2x80x94ORxe2x80x2, xe2x80x94OCORxe2x80x2 or xe2x80x94COORxe2x80x2, wherein Rxe2x80x2 represents a C1-20 alkyl or alkoxy group or C2-20 alkenyl or alkenyloxy group, and those groups may be substituted by a C1-10 alkoxyl, acyl, acyloxy or alkoxycarbonyl group and one or more hydrogen atoms contained in these groups may be substituted by one or more fluorine atoms, and in the case of forming an asymmetric carbon by the substitution or branching, it may form an optically active form or racemic form, with the proviso that (1) if Za represents a group represented by the general formula (IIa), b is 0, if Za represents a group represented by the general formula (IIb), a is 0, and if Za represents a fluorine atom, chlorine atom, trifluoromethoxy group, C1-7 alkoxyl group or C1-20 alkyl, alkoxyl, alkenyl or alkenyloxy group which may be substituted by from 1 to 7 fluorine atoms, a is 1; (2) if Za represents the group represented by the general formula (IIa), ring C represents a 1,4-phenylene group which may be substituted by fluorine atom and Zb represents a fluorine atom, chlorine atom, trifluoromethoxy group or an alkyl or alkoxyl group which may be substituted by fluorine atom, Lc represents xe2x80x94CH2CH2CH2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90CHCH2CH2xe2x80x94, xe2x80x94CH2CH2CHxe2x95x90CHxe2x80x94, xe2x80x94CH(CH3)CH2xe2x80x94, xe2x80x94CH2CH(CH3)xe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94, xe2x80x94CF2xe2x80x94 or xe2x80x94OCF2xe2x80x94 and/or at least one of X1 to X6 represents a fluorine atom; (3) if Za represents an alkyl or alkoxyl group, at least one of X1 to X6 represents a fluorine atom and/or Lc represents xe2x80x94CH2CH2CH2CH2xe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94, xe2x80x94CF2Oxe2x80x94 or xe2x80x94OCF2xe2x80x94; (4) if Za represents a fluorine or chlorine atom, La represents a single bond: and if ring A represents a 1,4-phenylene group which may be substituted by fluorine atom, b represents 0, or b represents 1 and Lb represents a single bond; and (5) if a and b each represent 0, X1 represents a fluorine atom and X2to X6 each represent a hydrogen atom; and if Lc represents a single bond, Zb represents fluorine atom, chlorine atom, hydrogen atom, trifluoromethoxy group, alkenyl group, alkenyloxy group, cyanato group or cyano group.
2. The compound according to Clause 1 above, wherein in the general formula (I) a and b each represent 1.
3. The compound according to Clause 1 above, wherein in the general formula (I) a is 1, b is 0 and Za is a group selected from the group consisting of fluorine atom, chlorine atom, trifluoromethoxy group, and C1-20 alkyl, alkoxyl, alkenyl or alkenyloxy group which may be substituted by C1-7 alkoxyl group or from 1 to 7 fluorine atoms.
4. The compound according to Clause 1 above, wherein in the general formula (I) a is 1, b is 0 and Za is a group represented by the general formula (IIa).
5. The compound according to Clause 1 above, wherein in the general formula (I) a and b each are 0 and Za represents a group represented by the general formula (IIa).
6. The compound according to Clause 1 above, wherein in the general formula (I) a and b each are 0 and Za represents a group represented by the general formula (IIb).
7. The compound according to any one of Clauses 1 to 6 above, wherein La, Lb, Lc and Ld in the general formula (I) each independently represent a group selected from the group consisting of xe2x80x94CH2CH2xe2x80x94 and single bond.
8. The compound according to any one of Clause 1 to 4 and 7 above, wherein ring A in the general formula (I) represents a group selected from the group consisting of trans-1,4-cyclohexylene group, 1,4-phenylene group, 2-fluoro-1,4-phenylene group, 2,6-difluoro-1,4-phenylene group and trans-decahydronaphthalene-2,6-diyl group.
9. The compound according to any one of Clauses 1, 2, 7 and 8 above, wherein ring B in the general formula (I) represents a trans-1,4-cyclohexylene group.
10. The compound according to any one of Clauses 1 and 4 to 7 above, wherein rings C and D in the general formula (I) each independently represent a group selected from the group consisting of 1,4-phenylene group, 2-fluoro-1,4-phenylene group, 3-fluoro-1,4-phenylene group, 2,3-difluoro-1,4-phenylene group and 3,5-difluoro-1,4-phenylene group.
11. The compound according to any one of Clauses 1 to 3 and 7 to 9 above, wherein Za in the general formula (I) represents a group selected from the group consisting of C4-12 alkenyl group which may be substituted by from 1 to 3 fluorine atoms and C3-12 alkenyloxy group which may be substituted by from 1 to 3 fluorine atoms.
12. The compound according to any one of Clauses 1 to 3 and 7 to 9 above, wherein Za in the general formula (I) represents a group selected from the group consisting of C1-12 alkyl or alkoxyl group which may be substituted by from 1 to 7 fluorine atoms.
13. The compound according to Clause 12 above, wherein Za in the general formula (I) represents a trifluoromethoxy group.
14. The compound according to any one of Clauses 1 to 13 above, wherein X1 in the general formula (I) represents a fluorine atom.
15. The compound according to Clause 14 above, wherein X2 in the general formula (I) represents a fluorine atom.
16. The compound according to Clause 2 or 3 above, wherein X1 and X2 in the general formula (I) each represent a fluorine atom.
17. A liquid crystal composition comprising a compound represented by the general formula (I) described in Clause 1 above.
18. The liquid crystal composition described in Clause 17 above for use in active matrix driving.
19. A liquid crystal device comprising as a constituent element a liquid crystal composition described in Clause 17 above.
20. An active matrix driving liquid crystal display device comprising a liquid crystal composition described in Clause 18 above.
In more detail, the present invention provides a novel liquid-crystalline compound which is a naphthalene derivative represented by the following general formula (I): 
In the foregoing general formula (I), Ra represents a C1-20 alkyl, alkoxy, alkoxyalkyl, alkenyl or alkenyloxy group which may be substituted by a C1-7 alkoxyl group or from 1 to 7 fluorine atoms. Ra preferably is a C1-7 straight-chain alkyl or alkenyl group. The alkyl group is preferably an unsubstituted alkyl group or an alkyl group terminated by a plurality of fluorine atoms, particularly an unsubstituted alkyl group. The alkenyl group, if the ring structure to which it is directly connected is a saturated ring, is preferably a 1-alkenyl group or 3-alkenyl group. In this case, the double bond is preferably at the end of side chain. Alternatively, the configuration of the double bond is preferably in trans-position. A particularly preferred example of the alkenyl group is a vinyl group or 3-butenyl group. Further, the hydrogen atom which is directly connected to the double bond is preferably substituted by a fluorine atom. Preferred examples of such a substituted alkenyl group include (E)-2-fluorovinyl group, 2,3-difluorovinyl group, 3-fluoro-2-propenyl group, 3,3-difluoro-2-propenyl group, 4-fluoro-3-butenyl group, and 4,4-difluoro-3-butenyl group. The alkenyl group, if the ring structure to which it is directly connected is an aromatic ring, is preferably a 3-alkenyl group. In this case, the double bond is preferably at the end of side chain. Alternatively, the configuration of the double bond is preferably in trans-position. A particularly preferred example of the alkenyl group is a 3-butenyl group or trans-3-pentenyl group.
a and b each represent 0 or 1 and satisfy the relationship axe2x89xa7b.
Rings A and B each independently represent a trans-1,4-cyclohexylene group, 1,4-phenylene group which may be substituted by one or more fluorine atoms, pyridine-2,5-diyl group, pyrimidine-2,5-diyl group, pyrazine-2,5-diyl group, pyridazine-3,6-diyl group, trans-1,3-dioxane-2,5-diyl group, trans-decahydronaphthalene-2,6-diyl group or tetrahydronaphthalene-2,6-diyl group. Preferred among these groups are trans-1,4-cyclohexylene group, 1,4-phenylene, 2-fluoro-1,4-phenylene group, 3-fluoro-1,4-phenylene group, 2,3-difluoro-1,4-phenylene group, 2,6-difluoro-1,4-phenylene group, and trans-decahydro naphthalene-2,6-diyl group. In particular, ring B is preferably a cyclohexane ring. Ring A, if a strong p-type liquid crystal composition is particularly required, is preferably a 2-fluoro-1,4-phenylene group or 2,6-difluoro-1,4-phenylene group. If a strong n-type (negative dieletric anisotropy) is particularly required, ring A is preferably a 3-fluoro-1,4-phenylene group or 2,3-difluoro-1,4-phenylene group.
La and Lb each independently represent xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2CH2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90CHCH2CH2xe2x80x94, xe2x80x94CH2CH2CHxe2x95x90CHxe2x80x94, xe2x80x94CH(CH3)CH2xe2x80x94, xe2x80x94CH2CH(CH3)xe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94, xe2x80x94CF2Oxe2x80x94, xe2x80x94OCF2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94 or single bond. Preferred among these groups are xe2x80x94CH2CH2xe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94, xe2x80x94CF2Oxe2x80x94, xe2x80x94OCF2xe2x80x94 and single bond, and xe2x80x94CH2CH2xe2x80x94 and single bond are particularly preferred. If La and Lb are present at the same time, at least one of them in more preferably a single bond.
X1 to X6 each independently represent a hydrogen atom or fluorine atom. In particular, X1 preferably represents a fluorine atom. If the liquid-crystalline compound is a p-type compound, one or more of X1 to X3 each are preferably a fluorine atom while X4 to X6 each are preferably a hydrogen atom. Further, if Za is a polar group such as fluorine atom, X1 and X2 or X1 to X3 each preferably represent a fluorine atom at the same time. If the liquid-crystalline compound is a n-type compound, at least one of X4 to X6 is preferably a fluorine atom. Alternatively, all X1 to X6 each represent a hydrogen atom. Alternatively, X1 is preferably a fluorine atom while the others are each preferably a hydrogen atom.
Za represents a fluorine atom, chlorine atom, trifluoromethoxy group, C1-7 alkoxyl group, C1-20 alkyl, alkoxyl, alkenyl or alkenyloxy group which may be substituted by from 1 to 7 fluorine atoms or group represented by the following general formula (IIa) or (IIb): 
Preferred among these groups are fluorine atom, trifluoromethoxy group, difluoromethoxy group, C1-7 straight-chain alkyl group, C1-3 straight-chain alkoxyl group, C4-7 straight-chain 3-alkenyl group, C3-7 straight-chain alkenyloxy group, and group represented by the foregoing general formula (IIa) or (IIb). Particularly preferred among these groups are fluorine atom, trifluoromethoxy group, methyl group, ethyl group, propyl group, butyl group, pentyl group, mothoxy group, ethoxy group, 3-butenyl group, trans-3-pentenyl group, allyloxy group, crotyloxy group, and group represented by the general formula (IIa).
In the general formula (IIa) or (IIb), Lc and Ld each independently represent xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90CHCH2CH2xe2x80x94, xe2x80x94CH2CH2CHxe2x95x90CHxe2x80x94, xe2x80x94CH(CH3)CH2xe2x80x94, xe2x80x94CH2CH(CH3)xe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94, xe2x80x94CF2Oxe2x80x94, xe2x80x94OCF2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94Cxe2x89xa1Cxe2x80x94 or single bond. Preferred among these groups are xe2x80x94CH2CH2xe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94, xe2x80x94CF2Oxe2x80x94, xe2x80x94OCF2xe2x80x94 or single bond. Particularly preferred among these groups are xe2x80x94CH2CH2xe2x80x94 or single bond. Further, if Lc and Ld are present at the same time, or if Lc and the foregoing La are present at the same time, at least one of them is preferably a single bond.
Rings C and D each independently represent a trans-1,4-cyclohexylene group, 1,4-phenylene group which may be substituted by one or more fluorine atoms, pyridine-2,5-diyl group, pyrimidine-2,5-diyl group, pyrazine-2,5-diyl group, pyridazine-3,6-diyl group, trans-1,3-dioxane-2,5-diyl group, trans-decahydronaphthalene-2,6-diyl group or tetrahydronaphthalone-2,6-diyl group. Preferred among these groups are trans-1,4-cyclohexylene group and 1,4-phenylene group which may be substituted by one or more fluorine atoms. Particularly preferred among these groups are 1,4-phenylene group, 2-fluoro-1,4-phenylene group, 3-fluoro-1,4-phenylene group, 2,3-difluoro-1,4-phenylene group, and 3,5-difluoro-1,4-phenylene group. In particular, if the liquid-crystalline compound is a p-type compound, rings C and D each are preferably a 3-fluoro-1,4-phenylene group or 3,5-difluoro-1,4-phenylene group.
Zb and Zc each independently represent a fluorine atom, chlorine atom, bromine atom, iodine atom, hydrogen atom, cyano group, xe2x80x94SCN, xe2x80x94OCN, xe2x80x94Rxe2x80x2, xe2x80x94ORxe2x80x2, xe2x80x94OCORxe2x80x2 or xe2x80x94COORxe2x80x2, wherein Rxe2x80x2 represents a C1-20 alkyl or alkoxy group or C2-20 alkenyl or alkenyloxy group, and these groups may be substituted by a C1-10 alkoxyl, acyl, acyloxy or alkoxycarbonyl group and one or more hydrogen atoms contained in these groups may be substituted by one or more fluorine atoms, and in the case of forming an asymmetric carbon by the substitution or branching, it may form an optically active form or racemic form.
Preferably, Zb and Zc each represent a fluorine atom, chlorine atom, hydrogen atom, trifluoromethoxy group, C1-7 alkoxyl group or C1-20 alkyl, alkoxyl, alkenyl or alkenyloxy group which may be substituted by from 1 to 20 fluorine atoms, cyanato group or cyano group. Preferred among these groups are fluorine atom, trifluoromethoxy group, difluoromethoxy group, C1-7 straight-chain alkyl group, C1-3 straight-chain alkoxyl group, C4-7 straight-chain 3-alkenyl group, C3-7 straight-chain alkenyloxy group or cyano group. Particularly preferred among these groups are fluorine atom, trifluoromethoxy group, methyl group, ethyl group, propyl group, butyl group, pentyl group, methoxy group, ethoxy group, 3-butenyl group, trans-3-pentenyl group, allyloxy group, crotyloxy group, and cyano group.
There are the following provisions:
(1) If Za represents the group represented by the general formula (IIa), b is 0, if Za represents the group represented by the general formula (IIb), a is 0, and if Za represents a fluorine atom, chlorine atom, trifluoromethoxy group, C1-7 alkoxyl group or C1-20 alkyl, alkoxyl, alkenyl or alkenyloxy group which may be substituted by from 1 to 7 fluorine atoms, a is 1;
(2) If Za represents the group represented by the general formula (IIa), ring C represents a 1,4-phenylene group which may be substituted by fluorine atom and Zb represents a fluorine atom, chlorine atom, trifluoromethoxy group or an alkyl or alkoxyl group which may be substituted by fluorine atom, Lc represents xe2x80x94CH2CH2CH2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90CHCH2CH2xe2x80x94, xe2x80x94CH2CH2CHxe2x95x90CHxe2x80x94, xe2x80x94CH(CH3)CH2xe2x80x94, xe2x80x94CH2CH(CH3) xe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94, xe2x80x94CF2Oxe2x80x94 or xe2x80x94OCF2xe2x80x94 and/or at least one of X1 to X6 represents a fluorine atom;
(3) If Za represents an alkyl or alkoxyl group, at least one of X1 to X6 represents a fluorine atom and/or La represents xe2x80x94CH2CH2CH2CH2xe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94, xe2x80x94CF2Oxe2x80x94 or xe2x80x94OCF2xe2x80x94;
(4) if Za represents a fluorine or chlorine atom, La represents a single bond; and if ring A represents a 1,4-phenylene group which may be substituted by fluorine atom, b represents 0, or b represents 1 and Lb represents a single bond; and
(5) If a and b each represent 0, X1 represents a fluorine atom and X2 to X6 each represent a hydrogen atom; and if Lc represents a single bond, Zb represents fluorine atom, chlorine atom, hydrogen atom, trifluoromethoxy group, alkenyl group, alkenyloxy group, cyanato group or cyano group.
As mentioned, there are a variety of compounds represented by the general formula (I). Preferred are those represented by the following general formulae (Ia) to (Ie) as classified by the structure of core moiety: 
wherein Ra, ring A, ring B, La, Lb, Zb, Zc and X1 to X6 are as defined in the general formula (I): ring C and ring D are as defined in the general formula (IIa) or (IIb); and Zd represents a fluorine atom, chlorine atom, trifluoromethoxy group, C1-7 alkoxyl group or C1-20 alkyl, alkoxyl, alkenyl or alkenyloxy group which may be substituted by from 1 to 7 fluorine atoms.
Particularly preferred among the compounds represented by the general formula (Ia) are those shown below. 
Particularly preferred among the compounds represented by the general formula (Ib) are those shown below. 
Particularly preferred among the compounds represented by the general formula (Ic) are those shown below. 
Particularly preferred among the compounds represented by the general formula (Id) are those shown below. 
Particularly preferred among the compounds represented by the general formula (Ie) are those shown below. 
In the foregoing general formulae, R is as defined above, and Rxe2x80x2 represents a C1-7 straight-chain alkyl group or C2-7 straight-chain alkenyl group, particularly vinyl group or 3-butenyl group.
Particularly preferred among the foregoing compounds are those represented by the general formulae (Iaaa) (Iaad), (Iaae), (Iacb), (Iagb), (Iaib), (Iana), (Ianb), (Iand), (Iapa), (Iapb), (Iata), (Iatb), (Iatd), (Iava), (Iavb), (Iawa), (Iawb), (Iawd), (IaAa), (IaAb), (IaAd), (IaCa), (IaCb), (Iaga), (IaGb), (IaGd), (IaJa), (IaJb), (IaJd), (IaNa), (IaNb), (IaNd), (IaPa), (IaPb), (IaPd), (IaTa), (IaTb), (IaTd), (IaVa), (IaVb), (IaVd), (IaZa), (IaZb), (IaZd), (Ibaa), (Ibab), (Ibad), (Ibca), (Ibcb), (Ibcd), (Ibea), (Ibeb), (Ibed), (Ibga), (Ibgb), (Ibgd), (Ibia), (Ibib), (Ibid), (Ibka), (Ibkb), (Ibkd), (Ibpa), (Ibpb), (Ibpd), (Ibsa), (Ibsb), (Ibsd), (Ibta), (Ibtb), (Ibtd), (Ibva), (Ibvb), (Ibvd), (Ibxa), (Ibxb) (Ibxd), (Icaa) to (Icim), and (Idaa) to (Idcm).
The compound represented by the general formula (I) of the present invention can be prepared by the following synthesis processes in combination depending on R, rings A and B, La and Lb.
[I] Process for the Synthesis of Compounds Represented by the General Formulae (Iaaa) to (Iafe)
(1) Compound prepared from a group represented by the following general formula (IIIa): 
wherein Rb represents an alkyl group as a key intermediate
(i) A naphthalene derivative represented by the following general formula (IVa): 
wherein Wa represents a halogen atom such as chlorine, bromine and iodine, preferably bromine atom; and Ya represents a phenolic hydroxyl group protected by methoxy or benzyloxy group, hydrogen atom or trifluoromethoxy group,
xe2x80x83is reacted with magnesium to produce a Grignard reagent or lithioated with an alkyl lithium such as butyl lithium to produce an organic metal reagent. The Grignard reagent or organic metal reagent thus prepared is then reacted with a 4-alkylcyclohexanone represented by the following general formula (Va): 
wherein Rb represents an alkyl group. Subsequently, the resulting cyclohexanol derivative is dehydrated in the presence of an acid catalyst to obtain a cyclohexenylnaphthalene derivative represented by the following general formula (IVa): 
wherein Rb represents an alkyl group; and Ya is as defined in the general formula (IVa). The cyclohexenylnaphthalene derivative thus obtained is subjected to catalytic reduction, optionally subjected to isomerization of cyclohexane ring, and then freed of Ya, if it is a protective group for phenolic hydroxyl group such as methoxy group, with hydrobromic acid to obtain a naphthol derivative represented by the foregoing general formula (IIIa).
(ii) The naphthol derivative (IIIa) obtained in the process (i) can be reacted with a halogenated alkyl or halogenated alkenyl in the presence of a base to obtain a compound represented by the general formula (Iafa) wherein R is an alkyl group.
(iii) The naphthol derivative (IIIa) obtained in the process (i) can be reacted with trifluoromethanesulfonic anhydride or trifluoromethanesulfonic acid chloride in the presence of a base such as pyridine to obtain a sulfonate represented by the following general formula (VIIa): 
wherein Rb is as defined above; and Tf represents a trifluoromethanesulfonyl group.
(iv) The sulfonate (VIIa) can be reacted with an organic metal reagent represented by the following general formula (VIIIa):
Rbxe2x80x94Maxe2x80x83xe2x80x83(VIIIa)
wherein Rb is as defined above; and Ma represents MgBr, MgCl, MgI or Li, preferably MgBr, in the presence of a nickel catalyst to obtain a compound represented by the general formula (Iaea) wherein R is an alkyl group. Preferred examples of the nickel catalyst employable herein include
dichlorobis(triphenylphosphine)nickel (II), dichloro[1,2-bis(triphenylphosphino)ethane]nickel (II), and tetrakis (triphenylphosphine)nickel (0).
(v) The naphthol derivative represented by the general formula (IIIa) can be reacted with carbon disulfide in the presence of a strong base, and then reacted with an alkylating agent to obtain a dithiocarbonic acid ester represented by the following general formula (IXa): 
wherein Rb is as defined above; and Rxe2x80x3 represents a lower alkyl group. Preferred examples of the strong base employable herein include hydrogenated alkaline metal such as sodium hydride, alkyl lithium such as butyl lithium, lithium amide such as lithium diisopropyl amide, and alcoholate such as potassium t-butoxide. Preferred examples of the alkylating agent employable herein include methyl iodide, ethyl iodide, methyl bromide, ethyl bromide, dimethyl sulfate, and methyl p-toluenesulfonate. The dithiocarbonic acid ester thus obtained can then be reacted with fluoride ion in the presence of a halonium ion generator to produce a compound represented by the foregoing general formula (Iaca) wherein R is an alkyl group. As the halonium ion generator there may be used N-iodosuccinic acid imide (NIS), N-bromosuccinic acid imide (NBS), N-chlorosuccinic acid imide (NCS), 1,3-dibromo-5,5-dimethylhydantoin (DBH) or the like. As the fluoride ion source there may be used tetrabutylammonium dihydrotrifluoride (TBAH2F3), hydrogen fluoride-pyridine complex (HF-Py), hydrogen fluoride-melamine complex (HF-mel) or the like. If the dithiocarbonic acid ester has an aromatic ring, the aromatic ring may be halogenated with halonium ion. In this case, the halide thus obtained can be lithioated with alkyl lithium such as butyl lithium, and then protonated to obtain the desired compound.
(vi) The compound represented by the general formula (IIIa) obtained in the foregoing process (i) can be reacted with ammonium in the presence of sodium hydrogensulfide to obtain a compound represented by the following general formula (Xa): 
wherein Rb is as defined above. The compound (Xa) can then be reacted with a fluorine source such as hydrofluoric acid in the form of nitrite represented by the following general formula (XIa): 
wherein Rb is as defined above, to obtain a compound represented by the general formula (Iaaa).
(vii) The compound represented by the general formula (XIa) obtained in the foregoing process (vi) can then be reacted with a chlorine source such as copper chloride (I) to obtain a compound represented by the foregoing general formula (Iaba) wherein R is an alkyl group.
(viii) The naphthol derivative represented by the general formula (IIIa) can be reacted with fluoride ion in the presence of a halonium ion generator in the form of thioformic acid ester represented by the following general formula (XIIa): 
wherein Rb is as defined above to produce a compound represented by the foregoing general formula (Iada) wherein R is an alkyl group. As the halonium ion generator there may be used N-iodosuccinic acid imide (NIS), N-bromosuccinic acid imide (NBS), N-chlorosuccinic acid imide (NCS), 1,3-dibromo-5,5-dimethylhydantoin (DBH) or the like. As the fluoride ion source there may be used tetrabutylammonium dihydrotrifluoride (TBAH2F3), hydrogen fluoride-pyridine complex (HF-Py), hydrogen fluoride-melamine complex (HF-mel) or the like. If the thioformic acid cater has an aromatic ring, the aromatic ring may be halogenated with halonium ion, in this case, the halide thus obtained can be lithioated with alkyl lithium such as butyl lithium, and then protonated to obtain the desired compound.
(ix) The naphthol derivative represented by the general formula (IIIa) can be fluorinated with one equivalent of a fluorinating agent such as N,Nxe2x80x2-difluoro-2,2xe2x80x2-dipyridinium bistetrafluoroborate and N-fluoxo-5-trifluoromethoxy pyridinium-2-sulfonate to obtain a compound represented by the following general formula (XIII): 
xe2x80x83and by-products represented by the following general formulae (XIVa) and (XVa): 
wherein Rb is as defined above.
(x) The naphthol derivative represented by the general formula (IIIa) can be fluorinated with two equivalents of a fluorinating agent such as 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2,2,2]octane bistetrafluoroborate and 1-fluoro-4-hydroxy-1,4-diazoniabicyclo[2,2,2]octane bistetrafluoroborate to selectively obtain a compound represented by the following general formula (XIVa): 
wherein Rb is as defined above. The compound (XIVa) can then be fluorinated with a fluorinating agent such as DAST and HF-pyridine to obtain a compound represented by the following general formula (XVIa): 
wherein Rb is as defined above. The compound (XVIa) can then be subjected to catalytic reduction to obtain a compound represented by the general formula (Iaad) wherein R is an alkyl group.
(xi) The compound (Iaad) obtained in the foregoing process (x) can be lithioated with butyl lithium, and then reacted with a fluorinating agent such as 1-chloromethyl-4-fluoro-1,4-diazoniabioyclo[2,2,2]octane bistetrafluoroborate and 1-fluoro-4-hydroxy-1,4-diazoniabicyclo[2,2,2]octane bistetrafluoroborate to obtain a compound represented by the general formula (Iaae) wherein R is an alkyl group.
(xii) The compound (XIIIa) shown in the foregoing process (ix) can be converted to a sulfonate in accordance with the foregoing process (iii), and then subjected to catalytic reduction to obtain a compound represented by the general formula (Iaab) wherein R is an alkyl group.
(xiii) The compound (XVa) shown in the foregoing process (ix) can be converted to a sulfonate in accordance with the foregoing process (iii), and then subjected to catalytic reduction to obtain a compound represented by the general formula (Iaab) wherein R is an alkyl group.
(xiv) The procedure of the foregoing process (vi) can be followed except that the compound represented by the general formula (IVa) is replaced by a compound represented by the following general formula (XVIIa): 
wherein Wa and Ya are an defined above to obtain a compound represented by the following general formula (XIXa): 
wherein Rb is as defined above, via a compound represented by the following general formula (XVIIIa): 
wherein Rb is as defined above. The compound represented by the general formula (XIXa) can be nitrated with a mixture of nitric acid and sulfuric acid, and then subjected to reduction to obtain a compound represented by the following general formula (XXa): 
wherein Rb is as defined above.
(xv) The compound (XXa) obtained in the foregoing process (xiv) can be reacted with a nitrite to produce a compound represented by the following general formula (XXIa): 
wherein Rb is as defined above, and then reacted with a fluorine source such as hydrofluoric acid to obtain a compound represented by the general formula (Iaac).
(xvi) The compound (XXIa) obtained in the foregoing process (xv) can be reacted with a chlorine source such as copper chloride (I) to obtain a compound represented by the general formula (Iabc) wherein R is an alkyl group.
(xvii) The compound (XXIa) obtained in the foregoing process (xv) can be reacted with water to obtain a compound represented by the following general formula (XXIIa): 
wherein Rb is as defined above.
(xviii) The compounds represented by the general formulae (XIIIa), (XVa) and (XXa) can be processed in accordance with the foregoing processes (ii) to (v), (vii) and (viii) to obtain compounds represented by the general formulae (Iabb), (Iabd), (Iacb), (Iacc), (Iacd) (Iadb), (Iadc), (Iadd), (Ieab), (Iaec), (Iaed), (Iafb), (lafc) and (Iafd) wherein R is an alkyl group.
(xix) The procedure of the processes (i) to (viii) can be followed except that the compound (iVa) is replaced by the compound (XXIIIa): 
wherein Wa, Ya, X1, X2 and X3 are as defined above, to obtain compounds represented by the general formulae (Iaaa) to (Iafe) wherein R is an alkyl group.
(2) Compound prepared from a group represented by the following general formula (IIIb): 
wherein Rc represents an alkenyl group as a key intermediate
(i) The naphthalene derivative represented by the general formula (IVa) is reacted with magnesium to produce a Grignard reagent or lithioated with an alkyl lithium such as butyl lithium to produce an organic metal reagent. The Grignard reagent or organic metal reagent thus prepared is then reacted with a compound represented by the following general formula (Vb): 
xe2x80x83dehydrated in the presence of an acid catalyst, optionally re-acetalated, subjected to catalytic reduction, and then deacetalated to obtain a naphthylcyclohexyl cyclohexanone derivative represented by the following general formula (XXIVb): 
wherein Ya is as defined above. The naphthylcyclohexyl cyclohexanone derivative (XXIVb) is reacted with a Wittig reagent represented by the following general formula (XXVb): 
xe2x80x83and then hydrolyzed with an acid to obtain a cyclohexane carbaldehyde derivative represented by the following general formula (XXVIb): 
The cyclohexane carbaldehyde derivative represented by the general formula (XXVIb) can be reacted with a Wittig reagent represented by the following general formula (XXVIIb):
CH2xe2x95x90PPh3,xe2x80x83xe2x80x83(XXVIIb)
and then freed of phenolic hydroxyl group of Za to produce a compound represented by the general formula (IIIb) wherein Rb is a vinyl group. The cyclohexane carbaldehyde derivative (XXVIb) can be further reacted with the Wittig reagent (XXVb) twice, reacted with the Wittig reagent (XXVIIb), and then freed of phenolic hydroxyl group of Za to produce a compound represented by the general formula (IIIb) wherein Rb is a 3-butenyl group.
(ii) The compound (IIIb) obtained in the process (2)-(i) can be processed in accordance with the processes (1)-(i) to (1)-(viii) to produce compounds represented by the general formulae (Iaaa) to (Iafe) wherein R is an alkenyl group.
[II] Process for the Preparation of Compounds Represented by the General Formulae (Iaga) to (Iane)
(1) Compound prepared from a group represented by the following general formula (IIIc): 
wherein R in as defined above as a key intermediate
(i) The naphthalene derivative represented by the following general formula (IVa) is reacted with magnesium to produce a Grignard reagent or lithioated with an alkyl lithium such as butyl lithium to produce an organic metal reagent which is reacted with trimethyl boron and then demethylated to obtain a boric acid derivative. The Grignard reagent or boric acid derivative thus produced can be reacted with a benzene derivative represented by the following general formula (Vc): 
wherein R is an defined above; and Yb represents a releasing group such as trifluoromethanesulfonyloxy of halogen atom such as chlorine, bromine and iodine, preferably trifluoromethanesulfonyloxy of bromine, in the presence of a transition metal catalyst, and then subjected to demethoxylation of Za to produce the desired compound.
Alternatively, the benzene derivative represented by the general formula (Vc) can be reacted with magnesium to produce a Grignard reagent or lithionatad with an alkyl lithium such as butyl lithium to obtain an organic metal reagent, reacted with trimethyl boron, demethylated to obtain a boric acid derivative, and then reacted with a benzene derivative represented by the following general formula (IVb): 
wherein Wb is as defined above, in the presence of a transition metal catalyst to produce the desired compound.
(ii) The procedure of the process [II]-(1)-(i) can be followed except that the compound (IIIc) is replaced by the compound (XVIIa) and the compound (IVb) is replaced by a compound represented by the following general formula (IVbxe2x80x2): 
wherein Zb is as defined above, to obtain a compound represented by the following general formula (XXVIIIb): 
wherein R is as defined above.
(iii) The procedure of the above processes [I]-(1)-(ii) to [I]-(1)-(xix) can be followed except that the compound (IIIa) is replaced by the compound (IIIb) and the compound (XVIIIa) is replaced by the compound (XVIIIb) to obtain compounds represented by the general formulae (Iaga) to (Iane).
[II] Process for the Preparation of Compounds Represented by the General Formulae (IaGa) to (IaMe), (IaZa) to (IaZe), (Ibaa) to (Ibde) and (Ibva) to (Ibye)
The procedure of the above process [I] can be followed except that the compound (Va) is replaced by compounds represented by the following general formulae (Vd) to (Vg): 
wherein Rb is as defined above, and the compound (Vb) is replaced by compounds represented by the following general formulae (Vdxe2x80x2) to (Vgxe2x80x2): 
to obtain compounds represented by the general formulae (IaGa) to (IaMe), (IaZa) to (IaZe), (Ibaa) to (Ibde) and (Ibva) to (Ibye).
[IV] Process for the Preparation of Compounds Represented by the General Formulae (IaAa) to (IaFe), (IaNa) to (IaSe), (IaTa) to (IaXe) and (Ibsa) to (Ibue)
The procedure of the above process [I] can be followed except that the compound (Va) is replaced by compounds represented by the following general formulae (Vh) to (Vk): 
wherein Rb is as defined above, and the compound (Vb) is replaced by the foregoing general formulae (Vdxe2x80x2) to (Vgxe2x80x2) to obtain compounds represented by the general formulae (IaAa) to (IaFe), (Iana) to (IaSe), (IaTa) to (IaXe) and (Ibsa) to (Ibue).
[V] Process for the Preparation of Compounds Represented by the General Formulae (Iana) to (Iase), (Iata) to (Iaye), (Ibea) to (Ibhe), (Ibfa) to (Ibme) and (Ibna) to (Ibqe)
The procedure of the above process [II] can be followed except that the compound (Vc) is replaced by compounds represented by the following general formulae (Vm) to (Vr): 
wherein R and Yb are as defined above, to obtain compounds represented by the general formulae (Iana) to (Iase), (Iata) to (Iaye), (Ibea) to (Ibhe), (Ibfa) to (Ibme) and (Ibna) to (Ibqe).
[VI] Process for the Preparation of Compounds Represented by the General Formulae (Icaa) to (Icch)
(i) The procedure of the above process [I]-(i) can be followed except that the compound (Va) is replaced by the compound represented by the general formula (Vf) to obtain a compound represented by the following general formula (XXIVa): 
The procedure of the process [I]-(1)-(ix) can be followed except that the compound (IIIa) in replaced by the compound (XXIVa) to obtain compounds represented by the following general formulae (XXVa) and (XXVIa): 
The compounds (XXIVa), (XXVa) and (XXVIa) can be reacted with trifluoromethanesulfonic acid anhydride or trifluoromethane sulfonic acid chloride in the presence of a base such as pyridine to obtain a sulfonate which is then allowed to undergo cross coupling reaction with a compound represented by the following general formula (XXVIIa): 
wherein Rf represents a hydrogen atom, fluoro group, trifluoromethoxy group, difluoromethoxy group or methoxy group; and E represents a hydrogen atom or fluorine atom, in the presence of a transition metal catalyst to produce compounds represented by the general formulae (Icaa) to (Icaf), (Icba) to (Icbf), (Icca) to (Iccf), (XXVIIIa) and (XXIXa): 
wherein E is as defined above.
The compound (XXVIIIa) thus obtained can be deprotected with hydrobromic acid, and then reacted with trifluoromethanesulfonic acid anhydride or trifluoromethane sulfonic acid chloride in the presence of a base such as pyridine to obtain a sulfonate which is then reacted with copper cyanide (I) or reacted with sodium cyanide or potassium cyanide in the presence of a transition metal catalyst to obtain compounds represented by the general formula (Icag), (Icah), (Icbg), (Icbh), (Iccg) and (Icch).
[VII] Process for the Preparation of Compounds Represented by the General Formulae (Icda) to (Iceh)
The procedure of the above process [VI] can be followed except that the compound (Vf) is replaced by the compound (Vk) to produce compounds represented by the general formulae (Icda) to (Iceh).
[VIII] Process for the Preparation of Compounds Represented by the General Formulae (Icfa) to (Icgh)
(i) The procedure of the above process [II]-(1)-(i) can be followed except that the compound (Vc) is replaced by the compound (Vp) to obtain a compound represented by the following general formula (XXXa): 
(ii) The procedure of the above process [VI] can be followed except that the compound (XXIVa) is replaced by the compound (XXXa) to obtain compounds represented by the general formulae (Icfa) to (Icgh).
[IX] Process for the Preparation of Compounds Represented by the General Formulae (Icha) to (Ichm), (Icia) to (Icim), (Idba) to (Idbm) and (Idca) to (Idcm)
The procedure of the above process [VIII] can be followed except that the compound (Vp) is replaced by compounds represented by the general formulae (Vq), (Vr) and (Vs):
xe2x80x83Rxe2x80x94Ybxe2x80x83xe2x80x83(Vs)
to produce compounds represented by the general formulae (Icha) to (Ichm), (Icia) to (Icim), (Idba) to (Idbm) and (Idca) to (Idcm).
[X] Process for the Preparation of Compounds Represented by the General Formulae (Idba) to (Iefm)
The procedure of the above process [IX] can be followed except that the compound (XXVIIa) is replaced by a compound represented by the following general formula (XXVIIb): 
to produce compounds represented by the general formulae (Icfa) to (Icgh).
Specific representative examples of the compound (I) of the present invention thus produced will be set forth in Tables 1 to 3 below together with their phase transition temperature.
The effects exerted by the incorporation of the compound (I) in the liquid crystal composition will be described hereinafter.
The compound represented by the general formula (Ib-1) set forth in Table 1: 
is added to a low viscosity host liquid crystal (H) having a wide operating temperature range, particularly a host liquid crystal (H) suitable for active matrix driving represented by the following general formula: 
in an amount of 20% to prepare a nematic liquid crystal composition (M-1). The upper nematic phase temperature limit (TNxe2x88x921) was 98.2xc2x0 C. The nematic liquid crystal composition (M-1) was allowed to stand at a temperature of 150xc2x0 C. for 20 hours, and then measured for TNxe2x88x921. The results were 97.8xc2x0 C., demonstrating that the nematic liquid crystal composition (M-1) showed little or no change of TNxe2x88x921 from before heating. The nematic liquid crystal composition (M-1) was irradiated with ultraviolet rays for 20 hours. However, the nematic liquid crystal composition (M-1) showed no change of TNxe2x88x921. The composition was then measured for voltage holding ratio. As a result, the composition exhibited a sufficiently high voltage holding ratio similarly to the host liquid crystal (H) during preparation, after heating and after irradiation with ultraviolet rays.
Subsequently, the nematic liquid crystal composition (M-1) was filled in a TN cell having a thickness of 4.5 xcexcm to prepare a liquid crystal device. The liquid crystal device was then measured for electro-optical properties. The results are as follows:
On the other hand, the physical properties and electro-optical properties of the host liquid crystal (H) alone are an follows:
The term xe2x80x9cresponsexe2x80x9d as used herein is meant to indicate the response time shown during the application of voltage at which the rise time (xcfx84r) and the drop time (xcfx84d) are equal to each other. The results show that the compound (Ib-1) exhibits a smaller dielectric anisotropy than the host liquid crystal (H) and a threshold voltage drop of about 10% from the host liquid crystal (H).
The compound represented by the general formula (Ib-2) set forth in Table 1: 
was then added to the host liquid crystal (H) in the same amount as mentioned above (20%) to prepare a liquid crystal composition (M-2).
TNxe2x88x921 of the nematic liquid crystal composition (M-2) and the electro-optical properties of the liquid crystal device prepared in the same manner as above from the composition (M-2) are as follows:
It can thus be seen that the compound (Ib-2) exhibits a smaller dielectric anisotropy than the host liquid crystal (H) and a threshold voltage drop of about 20% from the host liquid crystal (H)
The nematic liquid crystal composition (M-2) was then subjected to thermal stability test and ultraviolet ray irradiation test in the same manner as the composition (M-1). As a result, the composition (M-2) showed no change of TNxe2x88x921 after these tests. The nematic liquid crystal composition (M-2) was then measured for voltage holding ratio. As a result, the composition (M-2) exhibited a sufficiently high voltage holding ratio during preparation, after heating and after irradiation with ultraviolet rays.
As mentioned above, the compound represented by the general formula (I) is very useful in the preparation of a liquid crystal composition having (a) a wide nematic phase operating temperature range, (b) a threshold voltage low enough to drive at a low voltage, (c) a quick response and (d) a voltage holding ratio high enough for active matrix driving.
The compound represented by the general formula (Ic-7) set forth in Table 2: 
was added to a host liquid crystal composition (H) having a wide operating temperature range and a low viscosity which can be used also in active matrix driving in an amount of 20% by weight to prepare a liquid crystal composition (M-3). The physical properties of the host liquid crystal composition (H) and the electro-optical properties of the liquid crystal device prepared therefrom are as follows:
TNxe2x88x921: 116.7xc2x0 C.
TC-N: +11xc2x0 C.
Threshold voltage 2.14 V
Dielectric anisotropy (xcex94∈): 4.8
Birefringence index (xcex94n): 0.090
For the measurement of threshold voltage (Vth), the nematic liquid crystal composition is packed into a TN cell having a thickness of 6 xcexcm. The measurement is effected at a temperature of 20xc2x0 C.
The physical properties of the nematic liquid crystal composition (M-3) and the electro-optical properties of the liquid crystal device prepared therefrom are as follows:
TNxe2x88x921: 120.0xc2x0 C.
TC-N: xe2x88x922xc2x0 C.
Threshold voltage 2.06 V
Dielectric anisotropy (xcex94∈) 5.5
Birefringence index (xcex94n): 0.110
It can thus be seen that the addition of the compound (Ic-7) makes it possible to raise the upper nematic phase temperature limit (TNxe2x88x921) by not lower than 3xc2x0. The nematic liquid crystal composition (M-3) was cooled to a temperature of xe2x88x9260xc2x0 C. to undergo crystallization. The nematic liquid crystal composition (M-3) thus crystallized was then measured for melting point (TC-N). The results were xe2x88x922xc2x0 C., demonstrating that the composition (M-3) exhibits a melting point drop of as much as 13xc2x0 from the host liquid crystal composition (H). Accordingly, the stable temperature range of nematic phase can be expanded by as much as about 16xc2x0. It can also be seen that the incorporation of the compound (Ic-7) makes it possible to increase the dielectric anisotropy of liquid crystal composition and lower the threshold voltage of liquid crystal composition. The increase in the birefringence index could be suppressed to 0.02 from that of the host liquid crystal (H).
The liquid crystal device was then measured for voltage holding ratio at room temperature and 80xc2x0 C. The results were extremely good at any of the two temperature ranges, demonstrating that it can be sufficiently used in active matrix driving.
A compound represented by the following general formula (R-1) having a structure similar to the compound (Ic-7) but having 1,4-phenylene group instead of 2,6-naphthylene group: 
was added to the host liquid crystal composition (H) in the same amount as mentioned above (20%) to prepare a liquid crystal composition (HR-1). The upper nematic phase temperature limit (TNxe2x88x921) of the liquid crystal composition (HR-1) was 101xc2x0 C., which is far lower than that of the composition (M-3) an expected. The liquid crystal composition (HR-1) exhibited a melting point (TC-N) of 5xc2x0 C., which in higher than that of the composition (M-3). Accordingly, the liquid crystal composition (HR-1) exhibited a nematic phase temperature range of as much as 25xc2x0 or more smaller than the composition (M-3).
It can thus be seen that the composition (M-3) exerts a better effect than the conventional compounds to obtain a liquid crystal composition having a wide operating temperature range, a low threshold voltage and a proper birefringence index.
The compound represented by the general formula (Id-1) set forth in Table 3: 
was added to a host liquid crystal composition (H) having a wide operating temperature range and a low viscosity in an amount of 20% by weight to prepare a liquid crystal composition (M-4).
The physical properties of the compound (Id-1) and the electro-optical properties of the liquid crystal device prepared therefrom are as follows:
TNxe2x88x921: 91.0xc2x0 C.
Threshold voltage (Vth) 1.94 V
Dielectric anisotropy (xcex94∈): 4.85
Response (xcfx84r=xcfx84d): 28.4 m sec.
Birefringence index (xcex94n): 0.112
It can thus be seen that the incorporation of the compound (Id-1) in an amount of 20% causes a slight drop of the upper nematic phase temperature limit (TNxe2x88x921) but makes it possible to lower the threshold voltage of the liquid crystal composition and drastically raise the birefringence index of the liquid crystal composition (by about 0.02 from that of the host liquid crystal composition (H)) without drastically deteriorating the response. Subsequently, the liquid crystal composition was allowed to stand at room temperature for 1 month. However, no crystallization or phase separation were observed. It can thus be seen that the compound (Id-1) has an excellent miscibility with the conventional liquid crystals. The liquid crystal composition (M-4) was cooled to a temperature of xe2x88x9215xc2x0 C. to undergo crystallization, and then measured for melting point (TC-N). The results were 14xc2x0 C.
On the other hand, a compound represented by the general formula (R-2) having a structure similar to that of the compound (Id-1) but having a biphenyl skeleton: 
was added to the host liquid crystal composition (H) in the same amount as mentioned above (20% by weight) to prepare a liquid crystal composition (HR-2). The liquid crystal composition (HR-2) thus prepared was then measured for physical properties and electro-optical properties in the same manner as mentioned above. The results are as follows:
TNxe2x88x921: 86.0xc2x0 C.
Threshold voltage (Vth): 1.86 V
Dielectric anisotropy (xcex94∈): 4.92
Response (xcfx84r=xcfx84d): 27.0 m sec.
Birefringence index (xcex94n): 0.096
The comparison of the liquid crystal composition (HR-2) with the liquid crystal composition (H-1) shows that the liquid crystal composition (HR-2) exhibits a slightly higher response and a slightly lower threshold voltage (Vth). However, the upper nematic phase temperature limit (TNxe2x88x921) of the liquid crystal composition (HR-2) showed a further drop. The liquid crystal composition (HR-2) also showed only a slight increase in birefringence index.
Subsequently, the compound represented by the general formula (Id-2) set forth in Table 1: 
was added to the liquid crystal composition (H) in the same amount as mentioned above (20%) to prepare a liquid crystal composition (M-5). The physical properties of the liquid crystal composition (M-5) and the electro-optical properties of the liquid crystal device prepared therefrom are as follows:
TNxe2x88x921: 85.1xc2x0 C.
Threshold voltage (Vth): 1.74 V
Dielectric anisotropy (xcex94∈): 5.7
Response (xcfx84r=xcfx84d): 31.1 m sec.
Birefringence index (xcex94n): 0.107
The comparison of the liquid crystal composition (M-5) with the liquid crystal composition (M-4) shows that the liquid crystal composition (M-5) exhibits a slightly lower TNxe2x88x921 and a slightly reduced birefringence index but has a quick response similarly to the liquid crystal composition (M-4) and a further drop of threshold voltage.
The compound represented by the general formula (Id-7) set forth in Table 3: 
exhibits a melting point of xe2x88x9216xc2x0 C. and a nematic phase up to 13xc2x0 C. On the contrary, the compound (Id-1) having a skeleton structure similar to that of the compound (Id-7) but having naphthalene ring not substituted by fluorine is a crystalline material having a melting point of 62.5xc2x0 C. which shows no liquid-crystallinity. The liquid crystal composition obtained by adding the liquid crystal composition (Id-1) to a widely used host liquid crystal showed TNxe2x88x921 of xe2x88x9212xc2x0 C. Thus, the compound (Id-7) exhibits a better liquid-crystallinity.
It can thus be seen that the compound represented by the general formula (Id-7) causes no deterioration of liquid-crystallinity despite of the drop of melting point due to the incorporation of fluorine in naphthalene ring.
The foregoing compound (Id-7) was added to the host liquid crystal composition (H) in an amount of 20% by weight to prepare a liquid crystal composition (M-6).
TNxe2x88x921: 86.0xc2x0 C.
TC-N: 12xc2x0 C.
Threshold voltage (Vth): 1.65 V
Dielectric anisotropy (xcex94∈): 6.5
Birefringence index (xcex94n): 0.107
Response (xcfx84r=xcfx84d): 28.8 m sec.
The incorporation of the compound (Id-7) in an amount of 20% causes a slight drop of the upper nematic phase temperature limit (TNxe2x88x921) but can provide a high speed response similarly to the host liquid crystal composition (H) and makes it possible to drastically lower the threshold voltage of the liquid crystal composition (by 0.3 V). Further, the birefringence of the liquid crystal composition can be drastically increased from the host liquid crystal composition (H).
The liquid crystal device was then measured for voltage holding ratio at room temperature and 80xc2x0 C. The results were good at any of the two temperature ranges, demonstrating that the liquid crystal device can be sufficiently used in active matrix driving.
It can thus be seen that the compound represented by the general formula (Id) of the present invention exerts a better effect than the conventional compounds to obtain a low viscosity, an excellent response, a large birefringence index, a wide nematic phase operating temperature range, and a low threshold voltage.
Accordingly, the compound (I), when used in admixture with other nematic liquid crystal compounds, can be preferably used as a liquid crystal material for field effect type display call such as TN type and STN type display calls, particularly liquid crystal material which can operate at a wide temperature range and can be driven at a low voltage. Further, the compound represented by the general formula (I) has no strongly polar group in its molecule and thus can easily provide a large specific resistivity and a high voltage holding ratio. Thus, the compound represented by the general formula (I) can also be used as a constituent of liquid crystal material for active matrix driving. The present invention provides a liquid crystal composition comprising as a constituent at least one of the compounds represented by the general formula (I) and a liquid crystal device comprising the liquid crystal composition.
Specific representative examples of the nematic liquid crystal compound which can be used in admixture with the compound represented by the general formula (I) include phenyl benzoate derivative, phenyl cyclohexanecarboxylate derivative, biphenyl-4-yl cyclohexanecarboxylate derivative, phenyl cyclohexanecarbonyloxybenzoate derivative, phenyl cyclohexanecarboxylate derivative, phenyl cyclohoxylbenzoate derivative, cyclohexyl cyclohexylbenzoate derivative, biphenyl derivative, cyclohexylbenzene derivative, terphenyl derivative, bicyclohexane derivative, 4-cyclohexylbiphenyl derivative, 4-phenylbicyclohexane derivative, tercyclohexane derivative, 1,2-dicyclohexylethane derivative, 1,2-diphenylethane-derivative, 1,2-diphenylethine derivative, (2-cyclohexylethyl)benzene derivative, 4-phenethylbicyclohexane derivative, 4-(2-cyclohexylethyl)biphenyl derivative, 1-(4-phenyl)cyclohexyl-2-cyclohexylethane derivative, 1-(4-cyclohexylphenyl)-2-phenylethine derivative, phenylpyrimidine derivative, (4-biphenyl-4-yl) pyrimidine derivative, phenylpyridine derivative, and (4-biphenyl-4-yl)pyridine derivative. Particularly preferred for active matrix drive among these derivatives are biphenyl derivative, cyclohexylbenzene derivative, terphenyl derivative, bicyclohexane derivative, 4-cyclohexylbiphenyl derivative, 4-phenylbicyclohexane derivative, tercyclohexane derivative, 1,2-dicyclohexylethane derivative, 1,2-diphenylethane derivative, 1,2-diphenylethine derivative, (2-cyclohexylethyl)benzene derivative, 4-phenethylbicyclohexane derivative, 4-(2-cyclohexylethyl)biphenyl derivative, 1-(4-phenyl)cyclohexyl-2-cyclohexylethane derivative, and 1-(4-cyclohexylphenyl)-2-phenylethine derivative.